Join in the morning with buddy collecting seaweed (10)
I believe the answer is:
amalgamate
'join' is the definition.
(I've seen this before)
'in the morning with buddy collecting seaweed' is the wordplay.
'in the morning' becomes 'am'.
'with' is a charade indicator (letters next to each other).
'buddy' becomes 'mate' (I've seen this before**).
'collecting' indicates putting letters inside.
'seaweed' becomes 'alga' (I've seen this before).
'am'+'mate'='ammate'
'ammate' enclosing 'alga' is 'AMALGAMATE'.
(Other definitions for amalgamate that I've seen before include "get together" , "Merge" , "Compound" , "Mix" , "Join" .)